add overview, overlays and configuration pages

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+---
+layout: default
+title: Relx Overview
+---
+
+Overview
+========
+
+Relx is a tool that, given a specification, assembles
+releases. That is it makes an assessment of all of the Erlang/OTP Apps
+available to it and the constraints that you supply as part of your
+configuration and resolves a complete set of OTP Applications and
+thier versions for use in the release. This may be a bit hard to
+understand if you are not familiar with the way version resolutions
+work in package management systems. So lets look at an example.
+
+Lets say that you have the following OTP Applications
+
+     app1-1.2
+      with dependencies
+        app2
+        app5
+        app6
+    app1-1.3
+     with dependencies
+       app2
+       app6
+    app2-2.0
+     with dependencies
+       app6
+    app2-2.1
+     with dependencies
+       app6
+       app7
+    app3-2.0
+    app4-1.0.0
+    app5-3.0
+    app6-1.0
+     with dependencies
+       app3
+    app7-2.0
+
+This is the world of OTP Apps your Relx knows about (basically OTP
+Apps in the Library Directories you have specified). You have set a
+config that looks like the following:
+
+     {release, {awesome_supercool, "1.0"},
+        [{app1, "1.3", '>='},
+         {app2, "2.0", '>'},
+         app3]}
+
+When the Relx process has run you will end up with a complete
+release as follows
+
+    {release, {awesome_supercool, "1.0"},
+      [{app1, "1.3"},
+       {app2, "2.1"},
+       {app3, "2.0"},
+       {app6, "1.0"},
+       {app7, "2.0"}]}
+
+As you can see that is a fully realied view of your direct and
+transative dependencies based on the world that Relx knows about
+and the constraints that you specified in your configuration.